The method and apparatus of the present invention relate generally to the field of measuring and/or interacting with relationships between or among a plurality of media and/or spatial materials. For example, the present invention may be used to measure the quantity of fluid in a container.
The advent of the modern computer has greatly enhanced the fields of absolute and relative measurement and increased the speed at which spatial, geometric and temporal relationships may be calculated. Display technology now permits large scale visual reproduction of data and images representing multi-dimensional relative proximity. However, the current art still does not provide much of the useful, often critical, information that would be desirable.
For instance, oil companies have a great need for accurate information concerning the volume of oil in storage facilities. Many times, the oil companies are not aware of leaks in the storage facilities until after significant amounts of materials have been lost, and after serious environmental damage has already occurred. The leak rate may be so slow that the leak is not detectable through available monitoring techniques.
Additionally, most devices currently used for measuring the contents of containers do not provide a sufficiently high degree of accuracy. While devices with somewhat greater accuracy are available, these devices usually come at a prohibitively high cost.
The oil and gas industry is a prime example where inaccurate measuring devices are commonly used. Anyone experienced in the oil and gas industry knows that a used petroleum storage tank is never really safe. In fact, the incidence of welding accidents and maintenance personnel deaths when such tanks are inspected, cleaned or otherwise maintained are numerous. These accidents occur even when extra safety precautions are taken, such as applying so-called nitrogen "blankets" to the tanks.
U.S. Pat. No. 5,493,903 describes one type of measuring device that involves the application of a strain gauge sensor to the exterior wall of a tank. The greater the volume of a substance within the tank, the greater the force pushing on the tank walls. The greater the force pushing on the tank walls, the greater the deformation of the walls. This deformation is translated into a strain gauge reading. However, such strain-gauge sensors often provide inaccurate readings in exterior storage tanks, where temperature and pressure variations due to weather conditions and the like alter the readings over time of day and season.
U.S. Pat. No. 5,487,300 describes another type of measuring device that uses a pressure sensor connected to the opening of a tank for indicating the pressure of the liquid in the tank. A processor translates the pressure signal to a level signal. There may, however, be sludge or other measurement distorting material at the opening of the tank where the pressure sensor is located that can clog the opening and distort or interfere with the accuracy of the pressure reading.
Other known techniques for level detection include using a manual dip stick. However, the use of a dip stick requires that the stick be inserted perpendicularly to the bottom of the container. If the stick is inserted at an angle, the reading will be artificially high. Of course, use of a dip stick is not automatic in that it requires a person's presence to take the reading. Moreover, the person taking the reading, depending on the contents of the container, may have to wear a gas mask or other safety apparatus to prevent inhaling dangerous fumes, and such manual measurement presents an undesirable risk of bodily harm.
Still other efforts to measure container contents have focused on the use of "pulse radar level measurement" such as various products produced by the Ohmart Corporation of Cincinnati, Ohio. However, such devices are less accurate, generally more expensive and pose difficult installation problems. Further, they do not support desirable features such as off-site communication and control.
U.S. Pat. No. 4,774,403 describes a position measuring device using a triangulation scheme for position sensing. According to the invention, a laser light beam is reflected off the surface of container contents differently from when light is reflected off the bottom surface of the container. A lens of a sensor deflects the received light to different locations of a CCD linear array. Also, U.S. Pat. No. 5,337,289 discloses an acoustic surface mapping system useful in mapping the contours of solid container contents.
Current methods do not provide a sufficiently high degree of differentiation between different substances that may be within a tank, such as petroleum and water. Furthermore, current systems are ineffective for providing early warning of the theft of petroleum products from tanks, many of which are in remote locations. This is particularly problematic in underdeveloped countries where the additional hazard of intentional sabotage may greatly increase the incidence of severe environmental damage and product loss and where many industrialized nations now expend a large portion of their exploration and production budgets. Consequently, there exists a need for an improved means of acquiring container content information and promptly responding to such information.